JamVM looks like a nice and small JVM, suitable for Zaurus. It's already ported to ARM so I guess it should be fairly easy for a Zaurus devloper to port it?

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JamVM is a new Java Virtual Machine which conforms to the JVM specification version 2 (blue book). In comparison to most other VM's (free and commercial) it is extremely small, with a stripped executable on PowerPC of only ~135K, and Intel 100K. However, unlike other small VMs (e.g. KVM) it is designed to support the full specification, and includes support for object finalisation, Soft/Weak/Phantom References, the Java Native Interface (JNI) and the Reflection API.

And:

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ARM: ported and tested on the iPAQ running Linux (3950, with xscale PXA250 processor, though it should work on StrongARM). Little and Big Endian machines are supported, and soft/kernel FP emulation.